In Japanese Laid-Open Patent Publication No. 2000-334670, for example, when a plurality of operators perform screw tightening work by using a plurality of power tools (electric drivers) in assembly process of products in a factory, a power tool control system is described that screw tightening information is transmitted to each power tool via a network to achieve equalization of screw tightening quality.
Furthermore, in Japanese Laid-Open Patent Publication No. 11-320338, it is disclosed that data such as used hours or use times is recorded in a tool to estimate lifetime and the like of the tool.
By the way, when a very small screw is tightened into a small-sized product such as a camera, an electric driver for low-load work having a small tightening torque is suitable, even though it is a power tool belonging to the same category such as an electric driver. Alternatively, to tighten a relatively large screw into a large-sized product such as a car, an electric driver for high-load work having a large tightening torque is suitable. The screw tightening work includes not only the operation for tightening a male screw to a female screw previously formed but also an operation called self-tapping for directly tightening a male screw to a location where a female is not formed with forming a female screw at the same time. Still furthermore, there are cases that the power tool is operated continuously or intermittently depending on the work description or habitual practice of users, so that the degree of consumption of a battery varies in each case. Thus, to increase efficiency of assembly work, it is important to select and use the most suitable power tool according to the work description.